Checkvalve unit

ABSTRACT

A checkvalve ( 1 ) is provided with an inlet which can be connected to an operating system requiring a negative pressure, e.g. to a braking force amplifier ( 17 ), an outlet ( 3 ) which can be connected to a negative-pressure system producing a negative pressure, a main air channel ( 4 ) connecting the inlet and the outlet in a fluid manner and enabling an air flow in the direction of the outlet, a first checkvalve ( 9 ) installed in the main air channel ( 4 ), a single outside-air channel ( 5 ) which branches off downstream of the first checkvalve ( 9 ) and lets out into the atmosphere and a cross-sectional narrowing ( 7 ) in the manner of a venturi pipe ( 6 ), a venturi channel ( 8 ) connecting the cross-sectional narrowing ( 7 ) upstream of the first checkvalve ( 9 ) to the main air channel ( 4 ) and a second valve ( 10 ) located between the inlet ( 2 ) and the cross-sectional narrowing ( 7 ) in the main air channel ( 4 ) or in the venturi channel ( 8 ). A shut-off valve is located before or after the cross-sectional narrowing ( 7 ) in the outside-air channel ( 5 ) and is actuated as a function of the system pressure (p s ) prevailing in the operating system in such a manner that the connection to the atmosphere is established when a predetermined target pressure (P soll ) is exceeded and is interrupted when the pressure drops below this pressure.

The present application is a Continuation Application of ApplicationSer. No. 09/078,198, filed May 13, 1998, now U.S. Pat. No. 6,035,881.

FIELD OF THE INVENTION

The present invention relates to a checkvalve unit which is generallyused to connect an operating system, e.g. the braking force amplifier ofa vehicle braking system or the servomotor of the power steering system,of a vehicle requiring negative pressure to a suction system whichproduces negative pressure, e.g. the suction pipe or aspiration channelof a combustion engine. The checkvalve unit is to ensure that a negativepressure produced in an operating system is maintained, even when thepressure in the suction system rises or when the negativepressureproduction in the suction system is completely interrupted. The latteris the case for example when the vehicle engine is stopped.

A checkvalve unit comprises an inlet and an outlet connected to eachother via a main air channel. In the assembled state or in case ofutilization, the inlet is connected to the operating system and theoutlet to the suction system. A first checkvalve is located in the mainair channel. This prevents the negative pressure from escaping once ithas been produced in the operating system in case that pressure rises inthe suction system. Furthermore, one single outlet channel whichbranches off from the main air channel downstream of the firstcheckvalve and lets out into the atmosphere is provided with thecheckvalve unit in question. A venturi pipe or a narrowing of thecross-section is provided in this outer-air channel. This narrowing ofthe cross-section is connected via a channel, hereinafter the venturichannel, to the main air channel at a point located upstream of thefirst checkvalve.

Such a checkvalve unit, hereinafter the valve unit, is described in U.S.Pat. No. 5,291,916; DE 43 44 624 A1 and DE 43 10 761 C2. In the knownvalve units, it is a disadvantage that air is constantly sucked inthrough the outer-air channel. This is especially detrimental withcombustion engines where the air mass flowing through the choke valve ofthe air suction pipe is used for engine control or to optimize thecombustion process. In a valve unit described in U.S. Pat. No. 3,754,841the outer-air channel containing the venturi pipe can be closed off by asliding valve when the system pressure of the operating system hasreached its target value. The sliding valve is controlled bydifferential pressure. In addition, a membrane holding a plunger whichactuates the sliding valve is subjected on the one hand to the systempressure and on the other hand to a reference pressure. To produce thereference pressure, a venturi pipe is installed in a second outer-airchannel letting out into the atmosphere and connected to the suctionpipe of the engine. A connecting channel branches off from the narrowingpoint of the venturi pipe and influences the above-mentioned membranefrom one side. The second outer-air channel is permanently open, so thata stream of wrong air is constantly aspired by the suction pipe.Furthermore this valve unit can only be produced at high manufacturingand assembly costs.

OBJECTS AND SUMMARY OF THE INVENTION

Based on this, it is a principal object of the present invention topropose a valve unit which is simple in design and with which constantsuction of outside air is prevented.

According to the present invention, a cut-off valve is installed beforeor after the narrowing of the cross-section of the venturi pipe in thesingle outer-air channel, said cut-off valve being actuated as afunction of the system pressure prevailing in the operating system insuch a manner that the connection to the atmosphere is opened when apredetermined target pressure is exceeded and is interrupted when thispressure is not reached. The connection to the outer air is thus openonly when the system pressure exceeds a predetermined target pressure.As soon as the system pressure has dropped back to its target pressure,the outer-air channel is again shut off. An adulteration of the air massflowing through the checkvalve is thereby substantially prevented. As aseat valve, the checkvalve is made with two defined switching positions,i.e. one open and one closed position. Such a valve is easy to produceand is also less prone to failure than a sliding valve, in which asuitably sized valve bore must be precisely made.

In an example of an embodiment of the invention, the shutoff valve is anelectromagnetically actuated 2-way valve which is actuated by a controldevice which senses the system pressure by means of a pressure sensor.In this embodiment, it is first of all advantageous that the duration ofthe outer air arrival or of the open state of the outer-air channel canbe kept very short thanks to the electrical control. Generally speaking,opening the outer-air channel with a valve unit according to theinvention is only rarely needed, e.g. with repeated braking, after along stoppage or with rpm ranges of the engine which are rarely reached.An additional advantage of the electrical controls consists in the factthat analog electrical signals for other electrical or electromechanicalcontrol functions can be utilized for the actual negative pressure inthe braking force amplifier.

The shut-off valve may be a pneumatic shut-off valve which is actuatedby the difference in pressure between the system pressure and theatmospheric pressure. Such a checkvalve unit is simple in design if forno other reason than that the pressure difference is not between thesystem pressure and a separately produced reference pressure, but thatthe reference pressure used is the atmospheric pressure. Advantageousembodiments of the valve unit are characterized in particular by simpleand compact construction.

The invention is described in greater detail below through the examplesof embodiments described in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a functional diagram showing the utilization of a checkvalveunit with electromagnetic shut-off valve in a motor vehicle brakingsystem,

FIG. 2 shows the checkvalve unit of FIG. 1, but without theelectromagnetically actuated shut-off valve,

FIG. 3 is a schematic sectional representation of an embodiment withpneumatically controlled shut-off valve in a first operating state,

FIG. 4 shows the checkvalve unit of FIG. 3 in a second operating state,.

FIG. 5 shows the auxiliary braking system of a vehicle with a checkvalveunit as in FIGS. 3 and 4,

FIG. 6 shows a braking system according to FIG. 5, but with thecheckvalve unit connected in a different manner,

FIG. 7 shows a cut section of another embodiment of a checkvalve unit,

FIG. 8 shows a schematic cross-sectional view of another embodiment of avalve unit in a first operating state,

FIG. 9 shows the valve unit of FIG. 8 in a second operating state and

FIG. 10 is a diagram showing the dependence of the air mass flowingthrough the outside-air channel on the pressure in the suction pipe.

FIG. 11 is a diagram of volume flow Q through the outside air channelparticularly illustrating the volume flow when P_(SOLL) has beenreached.

DETAILED DESCRIPTION

Reference will now be made in detail to the presently preferredembodiments of the invention, one or more examples of which areillustrated in the drawings. Each example is provided by way ofexplanation of the invention, and not meant as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment can be used on another embodiment to yield a still furtherembodiment. It is intended that the present application include suchmodifications and variations.

As can be seen in FIGS. 1 and 2, a checkvalve unit according to theinvention (hereinafter valve unit 1 for short) comprises an inlet 2, anoutlet 3, a main air channel 4, an outside-air channel 5, a venturi pipe6 located in the outside-air channel with a cross-sectional narrowing 7which is normally found in a venturi pipe, a venturi channel 8connecting the cross-sectional narrowing 7 to the main air channel 4 aswell as a first checkvalve 9 and a second checkvalve 10. The firstcheckvalve 9 is located in the main air channel 4. Downstream of thefirst checkvalve 9, the outside-air channel 5 letting out into theatmosphere branches off from the main air channel. The venturi channel 8lets out upstream of the first checkvalve 9 into the main air channeland contains a second valve 10. The checkvalves 9,10 are plate valvesand each comprises accordingly a ring-shaped valve seat 12 and a valveplate 13 interacting with it. A pneumatically actuated 2-way valve isintercalated in the outside-air channel. The outside-air channel in theapplication shown in FIG. 1 is connected to the air filter 14 of the airsuction system of a vehicle via a circuit 15. The inlet 2 of the valveunit 1 is connected via a circuit 16 to the braking force amplifier 17of the auxiliary braking system of the vehicle. A pressure sensor 18 isconnected to the circuit 16 and is connected via a control circuit 19 toan electrical or electronic control device 20. The control deviceproduces a setting signal which is retransmitted via a control circuit22 to the solenoids 23 of the 2-way valve 21. The outlet 3 of the valveunit 1 is connected via a circuit 24 downstream of the throttle valve 25to the suction channel 27 leading to the combustion chamber of an engine26. The throttle valve 25 is thus subjected to air flow from the circuit15, the outside-air channel 5, the main air channel 4 and the circuit24, in the manner of a bypass. A constant air flow through this bypassis however prevented by the shut-off valve 21.

The valve unit shown in FIGS. 1 and 2 functions as follows: Only twodefined operating states are provided with the proposed valve unit. Inone operating state, the 2-way valve 21 is closed, in the otheroperating state it is open. In FIG. 2 a situation is shown in which the2-way valve 21 is closed. Starting from a situation where the pressureis balanced, e.g. after a long stoppage of the vehicle, air is suckedfrom the braking force amplifier 17 in direction of flow, mainly via thecheckvalve 9 as the engine is switched on. The 2-way valve is open asshown in FIG. 1. Thereby outside air is sucked in through the venturipipe 6. The air flowing through the outside-air channel is acceleratedwith the increased narrowing of the venturi pipe 6, and this causespressure to drop. At the narrowest point of the venturi pipe, thecross-sectional narrowing 7, the speed of flow is the greatest andtherefor the pressure of the air sucked in is correspondingly lowest.After the cross-sectional narrowing 7, the speed of flow is againreduced and the pressure rises accordingly. In the segment 29 locatedupstream before the checkvalve 9, the system pressure which is equal tothe system pressure p_(s) is lower -than the suction pipe pressureP_(SR) in the segment 30 of the main air channel 4 extending away fromthe venturi pipe 6. Due to these pressure relations, the valve plate 13of the checkvalve 9 is pressed against its valve seat 12 as the air flowlets up. The main air channel is thus closed off, and the air suckedfrom the braking force amplifier 17 is thereby sucked away via theventuri channel 8, at least towards the end of the evacuation process.When the system pressure p_(s) has dropped to a target value P_(soll),the control unit 20 actuates the solenoid 23 of the two-way valve 21 andmoves it into its second valve position, in which it closes off theoutside-air channel 5. If the system pressure P_(S) rises, e.g. becauseof multiple braking, the power flow to the solenoid 23 of the two-wayvalve is interrupted and the valve 21 is moved by a spring 32 into itsopen switch position. Outside air is then again sucked in through theventuri pipe 6, causing its negative pressure amplification to becomeactive.

The pressure and flow conditions are shown in form of two diagrams inFIGS. 10 and 11 for clarification. In the diagram of FIG. 10, the systempressure P_(S) is shown over the suction pipe pressure P_(SR) It can beseen that a continuous drop of P_(S) takes place up to the pre-settarget pressure P_(soll). The drop in the system pressure P_(S) ishowever greater than the drop of the pressure P_(SR) because of thenegative-pressure amplification through the venturi pipe. When P_(soll)has been reached, the outside-air channel is closed off, the twocheckvalves 9,10 are closed, because the pressure in segment 30 of themain air channel 4 is greater than P_(S). Only when the pressure P_(SR)becomes greater than P_(Soll), does further evacuation of the brakingforce amplifier 17 take place. FIG. 11 shows how the volume flow Qthrough the outside-air channel 5 stops suddenly when P_(Soll) has beenreached.

In the valve unit shown in FIG. 3, the outside-air channel 5 is closedoff by a directional seat valve 32 actuated by a pressure differencebetween the system pressure P_(S) and the atmospheric pressure. Thisdirectional seat valve 32 comprises a valve chamber 51 which issubdivided by a membrane 33 into an atmosphere chamber 34 and anegative-pressure chamber 35. The atmosphere chamber is connected on theone side to the atmosphere through an inlet opening 36, and on the otherside to the outside-air channel 5 through an outlet opening 37. Thenegative-pressure chamber 35 has a connection opening 41 through whichit is connected to the main air channel at a point upstream of thecheckvalve 10. The negative-pressure chamber 35 contains a helicalspring 38 which bears on the one side against the housing wall of thenegative-pressure chamber and on the other side on the membrane 33. Themembrane 33 has a central reinforced area 39 supporting a valve plunger40 which protrudes essentially at a right angle to the plane surface ofthe reinforced area and reaches through the connection opening. The freeend of the valve plunger 40 widens radially and is made in form of avalve plate 42. This valve plate 42 interacts with a valve seat 43surrounding the connection opening 37 outside the atmosphere chamber 34in form of a ring.

A system pressure P_(S) prevails in the negative-pressure chamber 35,while the atmospheric pressure prevails on the other side of themembrane, in the atmosphere chamber 34. The helical spring 38 isdesigned so that it exerts a force upon the membrane 39, said forcebeing slightly less than the force exerted in closing direction 44 dueto the pressure difference over the membrane. When the braking forceamplifier reaches the target system pressure P_(Soll), the valve plunger40 is pushed in closing direction and the valve plate 42 is accordinglypressed against the valve seat 43. The connection to the outside air isthen closed off. When, e.g. due to braking occurrences succeeding eachother in rapid sequence, the pressure P_(S) in the braking forceamplifier rises to such an extent that the pressure difference at themembrane 33 is equal to or smaller than the force exerted by the helicalspring 38, the membrane, and accordingly the valve plunger 40, moves inopening direction 45. The state shown in FIG. 4 is then reached. Thevalve plate 42 is lifted from the valve seat 43 and atmospheric air canbe sucked in through the inlet opening 36 and the outlet opening 37 viathe venturi pipe 6 in flow direction 28. In the cross-sectionalnarrowing 7 of the venturi pipe or in the venturi channel 8 followingit, a pressure drop occurs. Upstream of the venturi pipe 6 on the otherhand, the suction pipe pressure P_(SR) substantially prevails again. Dueto this pressure difference, the checkvalve 9 closes. The air suckedfrom the braking force amplifier goes therefore through the venturichannel 8. When the target system pressure P_(S) has again been reached,the pressure conditions over the membrane 33 are again such that thevalve plunger 40 moves in closing direction 44 and the outlet opening 37is closed.

FIG. 5 is an installation example for the valve unit described above.The main air channel 4 of the valve unit 1 is connected via a circuit 46to the braking force amplifier 17. The inlet opening 36 is connected viaa circuit 47 to the air filter 14. And to outlet 3 finally, a circuit 47a is connected which lets out into the suction channel 27 downstream ofthe throttle valve 25. The arrangement of FIG. 6 differs from that ofFIG. 5 in that the outside-air channel 5 is not connected to the airfilter but to the crank housing 48 of the engine.

In the embodiment shown in FIG. 7, a valve chamber 51 is also present,and is subdivided by a membrane 33 a into an atmosphere chamber 34 a andinto a negative-pressure chamber 35 a. The membrane 33 a has a central,reinforced area 39 a. The outside-air channel 5 lets out via a firstinlet opening 49 into the atmosphere chamber and emerges again via afirst outlet opening 50. A valve plunger 40 a protrudes essentially at aright angle from the flat side of the membrane 33 a or the reinforcedarea 39 a towards the atmosphere chamber 34 a and reaches through thefirst outlet opening 50 while its free end radially widens into a valveplate 42 a. The valve plate 42 a interacts with a valve seat 43 a whichsurrounds the first outlet opening in form of a ring. A helical spring38 a is installed in the negative-pressure chamber 35 a and presses themembrane 33 a in the opening direction 45. The main air channel 4 letsout into the negative-pressure chamber 35 a via a second inlet opening52 and emerges again via a second outlet opening 53. Finally the venturichannel 8 lets out via a third outlet opening 54 into thenegative-pressure chamber 35 a.

From the flat side of the reinforced area 39 a towards thenegative-pressure chamber 35 a, a second valve plunger 40 b extendsessentially at a right angle, its free end widening radially and forminga valve plate 42 b. This valve plate interacts with a valve seat 43 bsurrounding the third outlet opening 54 in form of a ring on the insideof the negative-pressure chamber 35 a. The valve plate 42 b and thevalve seat 43 b constitute the second checkvalve 10 a which is alsopresent in the previously described examples of embodiments and whichserves to shut off the venturi channel 8 against the main air channel 4.The second outlet opening 53 of the negative-pressure chamber 35 a issurrounded on the outside by a valve seat 55 in the form of a ring whichinteracts with a valve plate 55 a located outside the negative-pressurechamber 35 a. The valve plate 55 a and the valve seat 55 togetherconstitute the first checkvalve 9 a which is also present in theprevious examples of embodiments and is intercalated in the main airchannel 4. As seen in flow direction 28, the outside-air channel 5 letsout into the main air channel 4 before this valve. In the segment of themain air channel 4 following the second inlet opening 52 against theflow direction 28, another checkvalve 56 is installed which comprises avalve seat 56 a and a valve plate 56 b interacting with same.

The valve unit 1 according to FIG. 7 operates as follows: With thevehicle engine shut off, extensive pressure equalization takes place inthe course of the stoppage phase inside the valve unit. Only in thebraking force amplifier itself some negative pressure locked in by thecheckvalve 56 may still be present. Since the pressure conditions overthe membrane 33 a are balanced out, the membrane is moved by the helicalscrew 38 a into opening position, i.e. the first outlet opening 50 andthe third outlet opening 54 are open. If the engine is then started, anegative pressure pSR builds up in the suction channel 27. Because ofthe cross-sectional narrowing 7 in the venturi pipe 6 and the flowresistance connected with this, the main air mass is sucked away throughthe main air channel 4. The checkvalves 56 and 9 a located therein areopen. A partial air stream is however also sucked in through theoutside-air channel 5. As the system pressure pS decreases, the forceexerted upon the membrane 33 a increases due to the pressure differencebetween the system pressure and the atmospheric pressure. The spring, asdescribed earlier, is designed so that the membrane is moved in closingdirection 44 at a predetermined target system pressure pSoll. When thetarget system pressure has been reached, the outside-air channel 5 isclosed. This also applies to the venturi channel. An air flow in themain air channel only takes place under such conditions if the suctionpipe pressure pSR drops below the target system pressure.

The valve unit 1 shown in FIG. 8 has a particularly compact design. Allcomponents are placed in a common housing 60 which encloses a valvechamber 51 a. The valve chamber is subdivided by two separatingpartitions into an atmosphere chamber 34 b, a negative-pressure chamber35 b and a suction chamber 57. The atmosphere chamber 34 b is connectedvia an atmosphere opening 58 to the outside air. The separatingpartition located between the atmosphere chamber 34 b and thenegative-pressure chamber 35 b is a membrane 33 b with a centralreinforced area 39 b. The separating partition 62 between thenegative-pressure chamber 35 b and the suction chamber 57 has a passageopening 63. A valve plunger 59 in the form of a venturi pipe 6 extendsessentially at a right angle from the side of the reinforced membranearea 39 b away from the negative-pressure chamber 35 b. The valveplunger 59 reaches through the passage opening 63. A movable sealingmembrane 64 is provided between the outside circumference and theopening edge of the passage opening 63. This membrane hermetically sealsoff the negative-pressure chamber 35 b from the suction chamber 57. Ahelical spring 38 b is located in the negative-pressure chamber 35 b andbears on the one side upon the separating partition 62 and on the otherside on the reinforced membrane area 39 b and surrounds the valveplunger 59 at a radial distance. The venturi channel 8 extendsessentially radially to the valve plunger 59 and lets out on the oneside into the cross-sectional narrowing 7 and on the other side into thenegative-pressure chamber 35 b. The second check valve 10 b is locatedin the venturi channel. It is fixed on the circumferential surface ofthe valve plunger 59 together with a valve housing 65.

The free end of the valve plunger 59 is radially widened and formed intoa valve plate 66. The valve plate 66 interacts with a valve seat 69located on the housing wall 67 across from the separating partition 62.In addition to the passage opening 63, a connecting opening 68 is alsopresent in the separating partition 62 and is surrounded in the form ofa ring by a valve seat 69 located on the suction chamber side of theseparating partition 62. A valve plate 70 interacts with the valve seat69. The valve seat 70 and the valve seat 69 constitute the firstcheckvalve 9 b located in the main air channel 4. The main channel 4 isconstituted in the present case by the negative-pressure chamber 35 band the suction chamber 57. An inlet 2 is located at the beginning ofthe main air channel 4, and the outlet 3 forms its end. The outside-airchannel 5 on the other hand is constituted by the atmosphere chamber 34b and the interior space of the valve plunger 59, i.e. by the venturipipe 6. The shut-off valve closing the outside-air channel 5 is formedby the valve plate 66 and the valve seat 69.

The manner in which the valve unit according to FIG. 8 operates,starting from a pressure-balanced state, such as with a long enginestoppage, is described as follows: At first the valve plunger 59.is inits open position as shown in FIG. 9. Following the starting of theengine, the suction pipe pressure pSR builds up in the suction chamber57, producing a main air stream through the first checkvalve 9 b in themain air channel 4 and an accessory air stream through the venturi pipe6. Based on the venturi principle, a pressure drop then occurs betweenthe cross-sectional narrowing 7 of the venturi pipe 6 and thenegative-pressure chamber 35 b, causing a pressure drop going beyond thepressure produced by the suction channel of the engine. Accordingly thefirst checkvalve 9 b closes, so that an evacuation takes placeexclusively through the second checkvalve 10 b, the venturi channel 8and the suction chamber 57. With increasing evacuation, the pressuredifference at the membrane 33 b increases until finally a state isreached in which the force exerted in closing direction 44 upon themembrane 33 b is greater than the spring force of the helicoidal spring38 b. As a result the valve plunger 59 is moved into its closed positionshown in FIG. 8. A volume flow can then only take place when thepressure pSR in the suction chamber becomes greater than the targetpressure pS.

It should be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope and spirit of the invention. It isintended that the present invention includes such modifications andvariations as come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A check valve apparatus for maintaining negativepressure in an operating system, said check valve comprising: an inletconnectable to an operating system requiring a negative pressure, and anoutlet connectable to a system producing a negative pressure; a main airchannel establishing an air flow path between said inlet and saidoutlet; a first check valve disposed in said main air channel; anoutside air channel having one end in communication with said main airchannel at a location downstream of said first check valve in adirection of air flow through said main air channel to said outlet, saidoutside air channel in communication with atmospheric pressure at anopposite end thereof; a cross-sectional narrowing defined in saidoutside air channel with a venturi channel disposed between saidcross-sectional narrowing and said main air channel; a second checkvalve disposed in communication between said main air channel and saidcross-sectional narrowing; an automatic shut off valve disposed in saidoutside air channel to alternately isolate and open said outside airchannel to atmospheric pressure as a function of system pressure in theoperating system; and a sensor disposed to sense operating systempressure and a control device in communication with said sensor and saidshut off valve to control said shut valve in response to sensedoperating system pressure.
 2. The apparatus as in claim 1, wherein saidshut off valve comprises an electromagnetically operated valvecontrolled by a signal from said control device.
 3. The apparatus as inclaim 2, wherein said shut off valve comprises a two way solenoid valve.4. The apparatus as in claim 1, wherein said shut off valve is disposedupstream of said cross-sectional narrowing in said outside air channel.5. The apparatus as in claim 1, wherein said second check valve isdisposed in said venturi channel.